Supplemental info for CR-10-S4 and CR-10-S5:
Besides the build volume increase there are only a few differences between the CR-10 and CR-10-S4. Since the bed is larger, it has 2 supports underneath and 2 roller carriages. The S5 is larger and has dual Z motors, but besides that the assembly process is the same.
The adjustments to tighten the rollers are on the outsides of each rail. Flip the frame over (print surface down) and adjust. Do one side at a time until there is light drag on each wheel just like on the CR-10.
Next, you will have 1 of 2 belt idlers on the front of the machine.
To tension the belt, loosen the 4 bolts (2 on each side) and pry the bracket assembly away from the print bed, just like in the CR-10 assembly video.
Tiny Machines has added some spring isolators to the S4! These keep tension on the springs when the bed is raised for leveling and isolate the metal spring from the PCB bed which has been an issue on other printer models.